Stepper motor basic knowledge

The articles are displayed under several different titles, and there are many overlaps and cross-references between them, so I recommend that you read all the notes at least once.


Types of stepper motors

Broadly speaking, there are two types of stepper motors: unipolar and bipolar.

A bipolar motor has 4 wires, which are connected to two independent coils inside the motor, one pair for each coil.

There are also two types of unipolar motors: unipolar motors with 5 wires and unipolar motors with 6 wires. A 6-wire motor can also be called a hybrid motor. They are similar to 4-wire bipolar motors, except that an extra wire is connected in the center of each coil. If you want to use a 6-wire motor in bipolar mode, just ignore the wire connected to the center of the coil.


Motor specifications

The data sheet usually quotes the rated current, holding torque, coil resistance, coil voltage and microstep.

The voltage is irrelevant for all practical purposes. The important number is the rated current. The rated current refers to the current passing through each coil, and the current on the stepper motor drive board usually refers to the value. Holding torque is the maximum torque that can be used to resist rotation by inputting rated current to each coil of the stepper motor when the motor is stationary.

But the actual motor torque will decrease as the speed increases. The higher the motor speed, the faster the torque output decreases. Some manufacturers provide graphs showing how the torque changes with speed, and users can choose the motor they need based on this table.


Stepper Motor Driver Board

These are dedicated components designed to control stepper motors conveniently and efficiently. A4988 is a typical example frequently used by Arduino.

Generally speaking, the dedicated stepper motor driver board only needs two connections (plus GND) to the Arduino to get the step and direction signals.

Generally, dedicated stepper motor driver boards can limit the current in the motor, so that they can drive the motor with a higher voltage (A4988 is up to 35v) to achieve higher high-speed performance.

They usually have the ability of microstep. A4988 can perform 1 / 2, 1 / 4, 1/8 and 1/16 microstep. The default is a complete step. I believe that Easydriver using the same A4988 chip defaults to 1/16 microstep mode.


Choosing a motor and motor driver

The important specification of the motor is the torque of the motor. Generally speaking, the holding torque of the parameter, the larger the value, the larger the running torque of the motor. When selecting, choose a motor with sufficient torque margin.

After choosing the motor and knowing the required motor rated current, you can choose the appropriate stepper motor driver.

You should be aware that economical single-chip stepper drivers (such as A4988 and DRV8825) can only provide about 1 A and 1.5 A, respectively. If you have higher requirements for motors, you need to buy more expensive industrial level stepper driver.